Herd data on milk yield, herd size and disease incidence, as well as individual data for cows, such as breed, date of calving, parity and diseases during the study period, were retrieved from the SOMRS.
After exclusion of 1,657 herds where data on herd size was missing, 14,821 herds remained.
Regarding barren ewes, grouped logistic regression was used after transforming herd data to individual animal level (0 1) based on the rate and flock size, taking into account the herd effect in the analyses.
Stegeman et al. [ 4] estimated the time of virus introduction for each infected herd using data on contacts between infected herds and using serological findings on infected farms obtained shortly before depopulation [ 14].
Herd-level data on production, health and reproduction were retrieved from VÄXA Sweden and the study herds were representative of the source population.
In herd 2, data on 3,689 milkings on test days were used for estimating the initial model parameters.
In herd 1, data on 98,046 and 12,133 milkings registered from an automatic milking system (AMS) were used for model building and testing, respectively.
Herd level data on number of cows, AI-strategy, milk production, reproductive performance and health status from September 1st 2005 to August 31st 2006 were obtained from NADRS and SOMRS.
Such veterinarians would generally want to focus on possibilities for across-herd data analyses and, with time, be able to formulate meaningful disease control strategies based on empirical data at the herd level.
GR visited the herds and recorded data on housing system, environment, feeding and management.
